1. Field
The invention is in the field of controlling film flatness while viewing a still or freeze frame image on the film, and specifically to O-rings placed in specifically configured grooves for exerting lateral tension along the peripheral surfaces of the film at the viewing aperture to stretch and flatten the film.
2. Prior Art
The major disadvantage of film as a support for imaging media and reflectors versus plates is the difficulty of controlling film flatness. Previous means of controlling film flatness have been by the use of one or two pressure plates made of glass to put direct pressure on the film. Some problems with this are the added weight, increased number of optical surfaces and interference effects between these surfaces especially in the infrared spectrum. Film tensioning clamps have been used but these are complex and do not sufficiently apply desired lateral tension. Vacuum plates have been uses which have holes and grooves in the plates to distribute the vacuum suction to the film. These vacuum plates tend to deform the film where vacuum is applied.